Renewable fuse



Oct. 10, 1939. L. KELLNER RENEWABLE FUSE Filed July 16, 1937Il/IIMZIVIIII/llll INSULATION w.. z T2 Patented Oct. 10, 1939 UNITEDSTATES PATENT OFFICE 18 Claims.

This invention relates more particularly to irnprovements in an electricfuse structure of the cartridge type wherein a fuse element is enclosedwithin a tubular casing and has terminal blades v projecting from theopposite ends of the casing.

Important objects of the invention are, to facilitate renewal of thefuse; to provide for more secure locking of the fuse parts to thecasing; to provide for convenient unlocking of such parts from thecasing; and to provide for effective sealing of the casingr againstescape of re and at the same time permit escape of gas when the fuseblows, in order to prevent bursting of the casing.

Other objects of the invention will appear hereinafter.

In the drawing, Fig. 1 is a longitudinal sectional view of the improvedfuse structure;

Fig. 2 is a longitudinal section on the line 2 2 of Fig. 1;

Fig. 3 is a cross section on the line 3--3 of Fig. 1;

Fig. 4 is a view of one end of the fuse structure;

Fig. 5 is a view of the opposite end of the fuse structure. 5 Heretoforethe construction of a satisfactory renewable fuse of the present typehas been a diflicult problem. Fuses are required to pass underwritersinspection and tests. These tests are quite severe. In performing themcotton is packed around the fuse assembly and then the fuse is blown.The structure is subjected to quite a number of such tests and if, inany one of the tests, the cotton becomes ignited the fuse structure iscondemned. Among the causes of 5 failure of removable fuses to pass thetests are, insecure locking of the fuse parts at the ends of the casingwhich permits said parts to blow out of place under the pressure of thefuse blowout, imperfect sealing at the ends of the casing against escapeof sparks or flame, and insufficient venting of the casing to preventits bursting. Other faults in such fuses are difficult installation ofthe fuse in the casing and failure of the locking means for the fuseterminals to function properly after a fuse blow-out, owing to the heatand the pressure strain to which the locks are subjected. My inventionis directed to the correction of all of these faults in a renewablefuse.

The fuse structure includes a tubular casing 0 comprising a cylindricalbody I of stout, stiff insulation. A metal cap 2 is fitted over one endof the body I. Said cap is counterbored, as at 3, to receive the body Iand afford an end abutment for it. The cap forms an end wall 4 for thecasing. At the opposite end of the casing body (Cl. G-131) there is ametal collar or ferrule 5 counterbored, as at 6, to receive said end andform an abutment for it. The cap and collar closely lit the ends of thecasing body and are rigidly and permanently secured thereto by rivets'I.

The casing end wall 4 has an .elongated aperture or slot 8 through whichone of the fuse terminal blades projects. The outer end portion of thecap 2 is reduced in diameter and forms a seat or journal 9 for anothercap II) constitut ing a locking member rotatably fitted upon the seat 9and having an end wall II abutting the casing end wall 4. An annulargroove I2 is formed in the seat 9 and projections I3 on the cap I0protrude into said groove to hold the cap in place. The cap wall II hasa central aperture I4 of less diameter than the length of the slot 8 andalso has notches I5 diametrically arranged and opening into the apertureI4. The distance between the bottoms of these notches across theaperture is approximately equal to the length of the slot 8. At themargin of aperture i4 the cap wall II has two diametrically arranged,arcuate cam surfaces I6 sloping inward from the outer face of said wallto the notches I5. These cams function to lock one of the fuse tei-niiw1 to the casing and also seal the slot 8, be explained hereinafter. Atthe opposite end of the casing the collar 5 is counterbored from itsouter end, as at Il. In the bottom of this counterbore there is anannular groove I8 and the side of the counterbore there is an annulargroove I9. Groove I8 has a baffling function and groove I9 has a.locking function, as will be eX- plained hereinafter. The periphery ofthe fixed cap 5 and the periphery of the rotatable cap iare bothknurled, as at 20. All of the structure so far described comprises apermanently assembled casing unit.

A fuse unit extends through the casing and is detachably securedthereto. The fuse unit includes a fuse strip 2| and terminal blades 22and 23 joined to the ends of said strip. The terminals have reducedinner end portions or Shanks. 24 to one face of which the strip 2| isdetaohably secured. A rigid connection also joins the terminals to holdthem together in properly spaced relation after the fuse strip has beenblown. This rigid connection comprises a rigid bar 25 of insulation, andstii metal clips 26 riveted to the opposite ends of said bar. The clipsextend endwise from the bar and bear against the opposite face of theterminal shanks from the fuse strip. Bolts 2T, nuts 28 and washers 29secure the fuse strip and the clips to the terminal Shanks.

Terminal blade 22 projects outward through the slot il in the casing endwall li and bears a surrounding metal abutment flange 3@ to bear againstthe inner face of said wall to seal the slot 8. The flange is in thepresent instance formed of an elongated metal disk apertured to receivethe terminal blade and the blade and disk have a close, swaged iitrendering them in effect permanently integral and rigid and preventinges cape of gas through the aperture in the disk. Outwardly of the flange3G the opposite edges of the terminal blade have notches Si disposed topermit entry of the low ends of the cams l5 borne by the rotatablelocking cap lil. Thereby the flange may be drawn tight against the walll by locking rotation of the cap.

A metal closure disk 32 for the opposite end of the casing is aiiiXed tothe terminal 23. This disk also, in the present instance, is secured tothe terminal in the same manner as the ange disk 3G so that it surroundsthe terminal blade 23, forms in effect a permanent, rigid, integral partthereof and forms a gas-tight seal between the terminal and disk. At itsouter edge the disk is formed with an annular bafe ange 33 and a groove35 at the inner side of said flange. The flange is disposed to enter theannular groove i8 in the collar 5 and the groove 3E is disposed toreceive the annular flange forming the inner wall of the groove iii, fora desired battling effect. The periphery of disk 32 has an easy workingit in the counter-bore il.

A locking mechanism is mounted upon the outer face of the disk 32 tolock the fuse unit to the adjacent end of the casing. The mechanismincludes a number of flat locking elements or bolts and manuallyoperable means to shift them in unison into and out of the groove i9. Inthe present instance there are four of the locking elements and theirlocking portions are of segmental form, having arcuate outer edges whosecurvature corresponds approximately to that of the bottom of the grooveI9. The elements surround the terminal blade 23. One of the elements,designated 35, has inwardly diverging prongs 3% at opposite ends of itslocking portion and a short inwardly extending shank 3l! between saidprongs and formed with rack teeth 38 at one edge. Another element 39,diametrically disposed with reference to element 35 has similar prongs35 similarly disposed and diverging toward the prongs of element 35.Element 39 has a longer shank iii with rack teeth il in spacedopposition to rack teeth 33. The Shanks 3l and di! have portions ofreduced width slidably received in an aperture l2 in the terminal blades23. A pinion 13 rotatably mounted on the disk 32 meshes with the teethof both racks. Between the locking elements 35 and 39 are twodiametrically disposed locking elements @il of the same shape. They haveclearance notches or slots 45 to receive the opposite edges of theterminal blade. They also have oblique slots it formed and arranged toslidably receive the two pairs of prongs 3S.

The four locking elements may be made inexpensively of sheet metalstampings. They are operatively held in the same plane upon the disk 32and covered by an outer disk cil. The latter is held in place by a screwi8 and by the shaft Ll of the pinion 53. The screw is passed outwardlythrough the disk 32 and screwed into the disk il and is shouldered tohold the disks properly spaced. The pinion shaft extends through bearingapertures in both disks and is threaded at its ends to receive nuts 5E?and 5l. There may also be pins 52 borne by one or both disks at oppositesides of the pinion to hold the racks to the pinion. At the outer faceof the disk l'i there is an operating handle 53 for the pinion. Saidhandle has an eye fitted over the pinion shaft and keyed to it. A washeris disposed between the nut 5l and said eye. For convenience inoperating it the handle extends beyond the periphery of the collar 5. Onthe outer face of the disk 4l there is a locking bump 5ft over which thehandle snaps to yieldably hold the handle in a locking position and inan unlocking position.

The pinion i3 is Xed to rotate with its shaft sc that when the handle isswung in one direction the locking elements S5 and 39 will be projectedin unison into the annular groove I9 of the casing collar. Theangularity of the prongs 'J6 on said locking elements and of the slots46 on the other locking elements is such that when the elements 35 and39 are shifted outward the other locking elements will be camrnedoutward in unison therewith and into the groove I9. When the handle isrocked in the opposite direction all of locking elements will beretracted in unison from groove i9 to positions beneath the cover diskfil. The outer side of the groove I9 forms a keeper abutment 55 disposedin a plane at a right angle to the axis of the fuse casing, and thelocking elements are also in a plane at a right angle to said axis sothat the keeper abutment and the locking elements mutually engage in amanner `for positive locking. The locking margins of the segmentallocking elements also make an almost complete circle for maximum contactaround the keeper abutment.

The four locking elements arranged for radial movement form anekpansible locking means which serves to center the fuse unit within thecasing and also the cooperating re-bailiing ribs and grooves of thecasing and the closure disk. rThe four locking elements iitting withinthe groove i9 rotatively lock the closure disk and the terminal carryingsaid disk to the casing so that the terminal 23 carrying the closuredisk may be rotated slightly in either direction in order to aline itproperly with the contact clip which is to receive it. The flexibilityof the connection between the inner ends of the two terminals willpermit a slight rotation of the terminal 23 with respect to the terminal22, so that if the clips to receive these terminals are not quiteaccurately lined up with respect to each other, terminal 23 may berotated slightly in order to bring it into alinement with its contactclip.

The fuse strip i, the terminals 22 and 23, the rigid insulationconnection therebetween, the sealing flange Sil, the disks 32 and Lil,and the expansible loclnng mechanism are all held together as parts ofthe fuse unit. The fuse unit is installed in the casing by entering theterminal blade 22 through the open end of the casing defined by thecollar 5, and through the slot 8 in the opposite end wall fa and thenotches l5, which are first placed in register with slot 8 by rotationof the locking cap lil. When the flange 30 has bottomed on the end wall4 the locking cap is rotated to bring its cam iti into engagement withthe outer sides of the notches 3! of the terminal blade and cam theblade outward. This draws the iiange 3:'3 tightly against the Wall 4 toseal the slot 8. The sealing flange 33, the baffle flange 33 and theexpansible locking mechanism borne by the disk 32 are so spaced alongthe fuse unit that when the flange 3@ seats on the end wall 4 CTL thebaille flange 33 at the opposite end of the casing will be properlydisposed in the groove i8, and the locking segments will be in registerwith the keeper groove I9. Then the handle 53 is operated to expand thelocking segments into the keeper groove.

The fuse unit is securely locked to both ends of the casing in themanner described, and escape of re from the casing is eiectuallyprevented. One end of the casing is sealed by the ange 30. At the otherend escape of iire is eiectually prevented by the baffle means includingthe ang'e 33 and the grooves I8 and 34. At the same time, gas under theforce of the fuse blow-out will be forced past the baille means and pastthe disk 32, the locking segments and the disk 41 to relieve thepressure and prevent rupture of the casing. After a blow-out the fuseunit can be readily withdrawn after operating the handle 53 to retractthe locking segments and rotating the locking cap I!! to releaseposition. Owing to the provision of a rigid connection between the fuseterminals independent of the fuse strip the terminals are held in adenite spaced relation even after the fuse blows so that the terminalscan be withdrawn together and a new fuse strip can be readily attachedto the spaced terminals. The locking mechanism is also of such characteras to withstand numerous blow-outs.

What I claim is:

1. An electric fuse structure including a tubular casing open at one endand having an apertured end wall at its other end; a fuse unit extendingthrough said casing and insertible and removable through the open end ofthe casing and comprising a fuse strip, terminal members joined to theopposite ends of said strip and projecting from the opposite ends ofsaid casing and one of which terminal members projects through saidaperture in the casing end wall, a sealing abutment fixed to the latterterminal member to abut the inner face of said end wall to preventescape of iire through said aperture, a closure disk for the oppositeopen end of the casing to the other terminal member and adapted to fitwithin the said casing and to be removed therefrom with the fuse unit,and radially expansible locking means carried by the closure disk andcooperable with the inner surface of the casing to lock said closuredisk within the casing, and disposed to register for locking cooperationwhen said sealing abutment at the opposite end of the unit contacts saidend wall.

2. An electric fuse structure including a tubular casing having an endwall with an aperture; a fuse unit extending through said casing andinsertible and removable through the opposite end of the casing andcomprising a fuse strip, terminal members joined to the opposite ends ofsaid strip and projecting from the opposite ends of said casing and oneof which terminal members projects through said aperture in the casingend wall, a sealing abutment borne by the latter terminal member to abutthe inner face of said end wall to prevent escape of fire through saidaperture, a closure disk for the opposite end of the casing fixed to theother terminal member, and expansible locking and centering means borneby the latter terminal member and adapted to engage the casing to locksaid closure disk to the casing and center the fuse unit therein, anddisposed to register for locking cooperation with the casing when saidsealing abutment contacts said end wall.

3. An electric fuse structure including a tubular casing having an endWall With an aperture; a fuse unit extending through said casing andinsertible and removable through the opposite end of the casing andcomprising a fuse strip, terminal members joined to the opposite ends ofsaid strip and projecting from the opposite ends of said casing and oneof which terminal members projects through said aperture in the casingend wall, a sealing abutment borne by the latter terminal member to abutthe inner face of said end wall to prevent escape of re through saidaperture, a closure disk for the opposite end of the casing fixed to theother terminal member and expansible locking and centering means borneby the latter terminal member and adapted to engage the casing to locksaid closure disk to the casing and center the fuse unit therein, anddisposed to register for locking cooperation with the casing when saidsealing abutment contacts said end wall, and means carried by theclosure disk for operating the said expansible locking means to lockedand unlocked positions.

4. An electric fuse structure including a tubular casing having an endwall with an aperture; a fuse unit extending through said casing andinsertible and removable through the opposite end of the casing andcomprising a fuse strip, terminal members joined to the opposite ends ofsaid strip and projecting from the opposite ends of said casing and oneof which terminal members projects through said aperture in the casingend wall, a closure disk for the opposite end of the casing xed to theother terminal member, and expansible locking and centering means borneby the latter terminal member and adapted to engage the casing to locksaid closure disk to the casing and center the fuse unit therein, andmeans carried by the closure disk for operating the said expansiblelocking means to locked and unlocked positions.

5. An electric fuse structure comprising a tubular casing having an endwall with an elongated aperture; a fuse unit extending through saidcasing and comprising a fuse strip, terminal blades joined to theopposite ends of said fuse strip one of said blades projecting outwardthrough said aperture and the other projecting outward from the oppositeend of the casing, a rigid bar of insulation also joining said blades tohold them together as a unit when the fuse is blown, a sealing diskborne by and surrounding the terminal blade at said opposite end of thecasing and having an annular baiiie flange with its edge directedinwardly of the casing, the casing having an outwardly opening annularinternal groove into which said flange extends to baffle escape of fire,and a sealing flange borne by and surrounding the other terminal bladeto abut the inner face of said casing end wall to prevent escape of iirethrough said aperture; locking means borne by the casing and operable toforce and hold said sealing flange in sealing position; a plurality oflocking segments borne by the fuse unit at the outer face of saidsealing disk to shift radially of the casing axis, the casing having anannular inwardly facing keeper abutment outward of its said baillegroove and disposed to receive said segments when said sealing flangeabuts said wall at the opposite end of the casing, and lock-operatingmeans borne by the fuse unit to shift said segments in unison radiallyof the casing to lockably engage said keeper abutment, the fuse unitbeing withdrawable from the casing away from said end wall upon releaseof said locking means at opposite ends of the casing.

6. A fuse structure comprising a tubular casing, a fuse element withinsaid casing and having a terminal member projecting from one end of thecasing, a closure disk for said end of the casing borne by andsurrounding said terminal member and having an annular flange directedinwardly longitudinally of the casing, the casing having an internalgroove to receive said flange, to baflie escape of nre from the casing,and means to releasably lock said disk to the casing.

'7. A fuse structure comprising a tubular casing, a fuse element withinsaid casing and having a terminal member projecting from one end of thecasing, a closure disk for said end of the casing borne by said terminalmember; and locking means to secure said disk releasable to the casingcomprising a keeper abutment borne by the casing and facing inwardlylongitudinally of the casing, a plurality of locking members mounted onthe outer -l'ace of said disk to shift radially or the disk, andmanually operable means borne by the disk to shift said locking membersradially in unison into and out of locking relation to said keeperabutment.

8. A fuse structure comprising a tubular casing, a fuse element withinsaid casing and having a terminal member projecting from one end of thecasing, a closure disk for said end of the casing borne by said'terminal member; and locking means to secure said disk releasably tothe casing comprising a keeper abutment borne by the casing and facinglongitudinally inward thereof, a manually rotatable pinion borne by saiddisk, a plurality ot segmental loclnng elements mounted on the outerface of said disk to shift radially of the disk and including a pair ofdiametrically arranged elements with rack teeth engaged by said pinion,to shift the pair in unison into and out of locking relation to saidkeeper abutment, and others of said locking elements between said pairand having interlocking connections therewith to shift with said pair inunison into and out of locking relation to the keeper abutment.

9. An electric fuse structure comprising a tubular casing having an endwall with an elongated aperture, a fuse element within the casing havinga terminal blade projecting outward through said aperture, a sealingflange borne by and surrounding said terminal blade to abut the innerface of said end wall around the margin or" said aperture to preventescape of nre through the aperture, a rotatable locking cap securedpermanently to the end of the casing for rotation about the axis of thecasing and having an apertured end wall to receive the projectingterminal blade and having diametrically arranged locking cams formed onthe exterior surface of said end wall at the margin of said aperturetherein, and abutments borne by said terminal blade at opposite sideedges thereof and engageable by said cams to force and hold said sealingange against said end wall upon rotation of the locking cap in onedirection.

1G. A fuse structure comprising a tubular casing, a fuse element withinsaid casing and having a terminal member projecting from one end of thecasing, and a closure disk for said end of the casing borne by andsurrounding said terminal member and having an annular ange directedinwardly longitudinally of the casing, the casing having an internalgroove to receive said flange, to baiile escape or iire from the casing.

ll. An electric fuse structure comprising a tubular casing having an endwall with an elongated aperture, the other end of said casing beawa/reeing open; a fuse unit extending through said casing and comprising afuse strip, terminal blades joined to the opposite ends or said fusestrip one of said blades projecting outward from the opposite open endof the casing, a rigid bar of insulation also joining said blades tohold them together as a unit when the fuse is blown, a sealing flangeborne by and surrounding one terminal blade to abut the inner face ofsaid casing end wall to prevent escape of re through said aperture;rotary cam locking means permanently connected to the casing and adaptedto engage that portion of the terminal extending through said apertureand operable to force and hold said sealing flange in sealing positionagainst said end wall; a sealing disk ihred and surrounding the terminalblade at said open end of the casing and adapted to close said open end,a plurality of locking segments borne by the fuse unit at the outer faceof said sealing disk to shift radially of the casing axis, the casinghaving an annular inwardly facing keeper abutment disposed to receivesaid segments when said sealing iiange abuts said wall at the oppositeend of the casing, and lock-operating means borne by the fuse unit toshift said segments in unison radially of the casing to lockably engagesaid keeper abutment, the fuse unit, the sealing disk and the lockingsegments being withdrawable as a unit through the open end of the casingaway from said end wall upon release of said locking means at oppositeends of the casing.

l2. An electric fuse structure comprising a tubular casing open at oneend and having an apertured end wall at its other end; a ruse unit eX-tending through said casing and comprising a fuse strip, terminal bladesjoined to the opposite ends of said fuse strip one of said bladesprojecting outward through said aperture and the other projectingoutward through the opposite open end of the casing, a rigid bar ofinsulation also joining said blades to hold them together as a unit whenthe fuse is blown, a sealing disk xed to and surrounding the terminalblade at said opposite end of the casing and having an annular bailleflange with its edge directed inwardly of the casing, the casing havingan outwardly opening annular internal groove into which said ilangeextends to baiiie escape of rire, and a sealing flange borne by andsurrounding the other terminal blade to abut the inner face oi saidcasing end wall to prevent escape of nre through said aperture, lockingmeans adapted to engage the terminal and operable to hold said sealingflange in sealing position; a sealing disk locking means carried by thefuse unit at the outer face of said sealing disk and adapted to engagethe casing outward or its said baule groove and operable to lockedposition when said sealing flange abuts said end wall at the oppositeend of the casing, and means borne by the fuse unit to operate thesealing-disk locking means, the fuse unit and the sealing disk and its1iooking means being withdrawable as a unit from the casing away fromsaid end wall upon release of said locking means at opposite ends of thecasing.

13. An electric fuse structure comprising a tubular casing open at oneend and having an apertured end wall at its other end; a fuse unit eX-tending through said casing and comprising a fuse strip, terminal bladesjoined to the opposite ends of said fuse strip, one of said bladesprojecting outward through said aperture, and the other projectingoutward through the open end of the casing; a sealing ange carried byone terminal blade Within the casing to abut the inner face of the endwall of the casing to close the aperture therein; a sealing disk ixed tothe terminal blade at the open end of the casing and formed with anannular baille flange with its edge directed inwardly of the casing, thecasing being formed with an outwardly opening annular internal grooveinto which said flange extends to bale escape of fire; a sealing-disklocking means carried by the fuse unit at the outer face of said sealingdisk to engage the casing and center the sealing disk therein and lockit against longitudinal or transverse movement in the casing,

14. An electric fuse structure comprising a tubular casing open at oneend and having an apertured end wall at its other end; a fuse unitextending through said casing and comprising a fuse strip, terminalblades joined to the opposite ends oi said fuse strip, one of saidblades projecting outward through said aperture, and the otherprojecting outward through the open end of the casing; a sealing flangecarried by one terminal blade Within the casing to abut the inner faceof the end Wall of the casing to close the aperture therein; a sealingdisk fixed to the terminal blade at the open end of the casing andformed with an annular baiile flange with its edge directed inwardly ofthe casing, the casing being formed with an outwardly opening annularinternal groove into which said flange extends to baille escape of fire;a sealing-disk locking means carried by the fuse unit at the outer faceof the sealing-disk and comprising radially shiftable locking elementsto engage the internal surface of the casing and center the sealing diskin locked position within the casing.

15. An electric fuse structure including a tubular casing having an endwall with an aperture the other end of the casing being open; a fuseunit extending through said casing and insertible and removable throughthe open end of the casing and comprising a fuse strip, terminal membersjoined to the opposite ends of said strip and projecting from theopposite ends of said casing and one of which terminal members projectsthrough said aperture in the casing end wall, a sealing abutment borneby the latter terminal member to abut the inner face of said end wall toprevent escape of fire through said aperture, a closure disk for theopen end of the casing fixed to the other terminal member, andexpansible locking means borne by the latter terminal member and adaptedto engage the casing to rotatively lock said closure disk and theterminal carrying said disk to the casing.

16. An electric fuse structure including a tubular casing open at oneend and having an apertured end wall at its other end; a fuse unitextending through said casing and insertible and removable through theopen end of the casing and comprising a fuse strip, terminal membersjoined to the opposite ends of said strip and projecting from theopposite ends of said casing and one of which terminal members projectsthrough said aperture in the casing end wall, a sealing abutment fixedto) the latter terminal member to abut the inner face of said end wallto prevent escape of fire through said aperture,

70 a closure disk for the opposite open end ofv the casing rlxed to theother terminal member and adapted to close the said casing and to beremoved With the fuse unit, and locking means for said fuse unitcomprising a keeper abutment on the casing adjacent the open end thereofand facing longitudinally inwardly of the casing, and locking devicescarried by said closure disk and disposed to register with said keeperabutment when said sealing abutment at the opposite end of the unitcontacts said end wall and mounted on said disk to shift transversely ofthe axis of the casing into and out of locking relation to said keeperabutment.

17. An electric fuse structure including a tubular casing open at oneend and having an apertured end wall at its other end; a fuse unitextending through said casing and insertible and removable through theopen end of the casing and comprising a fuse strip, terminal membersjoined to the opposite ends of said strip and projecting from theopposite ends of said casing and one of which terminal members projectsthrough said aperture in the casing end wall, a sealing abutment xed tothe latter terminal member to abut the inner face of said end wall toprevent escape of re through said aperture, a closure disk for theopposite open end of the casing xed to the other terminal member andadapted to close the said casing and to be removed with the fuse unit,and locking means for said fuse unit comprising a keeper abutment onsaid casing adjacent to the open end thereof and facing longitudinallyinwardly of the casing, a plurality of locking members carried by saiddisk and spaced around the axis of the casing and disposed to registerwith said keeper abutment when said sealing abutment at the opposite endof the unit contacts with said end wall and mounted on said disk toshift into and out of locking relation to said keeper abutment, andmanually operable means borne by said disk to shift said locking membersinto and out of locking rotation to said keeper abutment.

18. An electric fuse structure including a tubular casing open at oneend and having an apertured end wall at its other end; a fuse extendingthrough said casing and insertible and removable through the open end ofthe casing and comprising a fuse strip, terminal members joined to theopposite ends of said strip and projecting from the opposite ends ofsaid casing and one of which terminal members projects through saidaperture in the casing end wall, a sealing abutment xed to the latterterminal member to abut the inner face of said end wall to preventescape of re through said aperture, a closure disk for the opposite openend of the casing fixed to the other terminal member and adapted toclose the said casing and to be removed with the fuse unit and having anannular ilange directed longitudinally inwardly of the casing, thecasing having an annular internal groove to receive said flange tobaille escape of fire from the casing, and locking means carried by theclosure disk and cooperable with the casing to lock said closure disk tothe casing, and disposed for locking cooperation with the casing whensaid sealing abutment at the opposite end of the unit contacts said endwall.

LOUIS KELLNER.

